Mapping of electrical potentials in the heart is now commonly performed, using cardiac catheters comprising electrophysiological sensors for mapping the electrical activity of the heart. Typically, time-varying electrical potentials in the endocardium are sensed and recorded as a function of position inside the heart, and then used to map a local electrogram or local activation time. Activation time differs from point to point in the endocardium due to the time required for conduction of electrical impulses through the heart muscle. The direction of this electrical conduction at any point in the heart is conventionally represented by an activation vector, which is normal to an isoelectric activation front, both of which may be derived from a map of activation time. The rate of propagation of the activation front through any point in the endocardium may be represented as a velocity vector. Mapping the activation front and conduction fields aids the physician in identifying and diagnosing abnormalities, such as ventricular and atrial tachycardia and ventricular and atrial fibrillation, which may result from areas of impaired electrical propagation in the heart tissue.
Localized defects in the heart's conduction of activation signals may be identified by observing phenomena such as multiple activation fronts, abnormal concentrations of activation vectors, or changes in the velocity vector or deviation of the vector from normal values. Examples of such defects include re-entrant areas, which may be associated with signal patterns known as complex fractionated electrograms. Once a defect is located by such mapping, it may be ablated (if it is functioning abnormally) or otherwise treated so as to restore the normal function of the heart insofar as is possible. As an illustration, cardiac arrhythmias including atrial fibrillation, may occur when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. Procedures for treating arrhythmia include disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals, such as by forming lesions to isolate the aberrant portion. Thus, by selectively ablating cardiac tissue by application of energy via a catheter, it is sometimes possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions.
A number of advantages may be obtained by providing a catheter having multiple electrodes to allow for mapping larger regions and/or for creating a plurality of lesions either simultaneously or without the need to reposition the catheter. One suitable configuration described in commonly assigned U.S. Pat. No. 6,961,602, which is herein incorporated by reference, employs a catheter having a multiray electrode assembly formed by a plurality of spines each carrying one or more diagnostic or ablation electrodes. The assembly has two or more spines, each having a proximal end attached at the distal end of the catheter body and a free distal end. Another configuration that has been employed is known as a basket-shaped electrode assembly. Examples are described in commonly assigned U.S. Pat. Nos. 5,772,590, 6,748,255 and 6,973,340, the entire disclosures of each of which are incorporated herein by reference. Basket catheters also employ a plurality of spines, which are connected at their distal end as well as the proximal end. In either configuration, the spines may be arranged in an expanded arrangement wherein at least a portion of each spine extends radially outwardly from the catheter body or in a collapsed arrangement wherein each spine is disposed generally along the longitudinal axis of the catheter body. The collapsed arrangement facilitates advancing the electrode assembly to the desired location in the patient's body, such as through the vasculature in a percutaneous approach. When the electrode assembly assumes the expanded arrangement, one or more of the electrodes on the spines are brought into contact with tissue to allow for measurement of electrical signals and/or ablation of tissue.
By employing multiple spines, these electrode assemblies are adapted to provide an array of electrodes to occupy a three dimensional space defined by the anatomy of the patient, such as a chamber of the heart or an ostium vessel for example. Generally, it would be desirable to deploy the spines, and correspondingly the electrodes, in a defined configuration to obtain any number of benefits, such as to provide coverage of the deployed area with certain density of electrodes, to provide concentrated coverage in a specific region, to help determine the location of the electrodes with respect to each other, to more closely conform to the volume in which it is deployed, or any others. However, conventional multiple spine electrode assemblies may not deploy with the spines in the intended configuration, creating a suboptimal array of electrodes. For example, in a multiray electrode assembly, the spines are secured in relation to each other only at the proximal end, while in a basket-shaped electrode assembly, they are secured only at their proximal and distal ends. As such, the spines may not assume their intended radial distribution, particularly at locations that are farther away from the secured ends. Notably, the spines may bunch together more closely or may splay apart to a greater degree than desired. The tendency of the multiple spine electrode assemblies to assume such unintended distributions may be exacerbated by irregularities in a patient's anatomy.
Accordingly, there is a need for an electrode array assembly that has improved stability. For example, it would be desirable to provide an electrode array assembly in which the electrodes have a greater tendency to remain in defined relationships with each other. The techniques of this disclosure as described in the following materials satisfy these and other needs.